Sigma possesses an unnamed ability that allows him to exchange information through physical touch. When he makes contact with another person, he can trade the information he most desires for the piece of information that person most desires, making it a mutual exchange rather than a one sided extraction. This power made him an exceptionally effective casino manager and a key operative for the Decay of the Angel, as reading the deepest wants of his guests gave him unparalleled control over every interaction. It also played a central role in the arc where he confronted a high ranking ability user authority figure to locate a page from the supernatural Book.

Sigma was written into existence using a page from a supernatural book that holds the power to rewrite reality. He emerged as a fully formed adult in a desert with no memories, no past, no biological parents, and no sense of self. Despite appearing to be in his early twenties, he has only existed for about three years at the time the series introduces him. This artificial origin is also reflected visually: his hair is split into two distinct colors, white and lavender, a design choice that mirrors his fragmented, created nature. His entire character arc revolves around the question of whether someone with no past can build a meaningful identity and find a place to truly belong.

After being exploited by various groups following his creation, Sigma was recruited by the leader of the Decay of the Angel, who offered him the role of General Manager at the Sky Casino, a high altitude establishment operating above Yokohama. For Sigma, the casino is far more than a job. It is the first and only home he has ever had. He has memorized the names, faces, and preferences of every guest who has passed through, and he manages the entire operation through sheer will and hard work rather than natural talent. His loyalty to the casino is total because without it, he has nothing. This emotional core is what makes Sigma such a compelling character and a popular choice for an anime plush toy among fans of the series.

Sigma's two most significant connections within the Decay of the Angel are with Nikolai Gogol and Fyodor Dostoevsky. His relationship with Nikolai is characterized by a strained tolerance, with Nikolai's chaotic and unpredictable nature contrasting sharply against Sigma's composed, controlled management style. His relationship with Fyodor is one of fearful deference. Fyodor recruited and empowered him but ultimately views Sigma as a tool rather than an equal, which sits in painful tension with Sigma's desperate need to feel that his existence has value. These dynamics have made Sigma a fan favorite for character analysis and ship discussion across the fandom, and his collectible anime plush form is often sought by fans who connected emotionally with his arc.

As of the most recent arcs in the manga, Sigma is alive. Following the fall of the Sky Casino and the intense battles at Meursault Prison involving the Armed Detective Agency, the Hunting Dogs, and the Decay of the Angel, Sigma survived and remained an active figure navigating the ongoing conflicts in Yokohama. His current position reflects the fallout from those events and continues to explore his search for purpose and belonging. Fans actively follow his status in ongoing manga chapters, making Sigma one of the more frequently discussed supporting characters in the fandom and one of the most requested subjects for handmade anime plush collectibles.